Abstract

The luminescence properties of highly strained, Sb-doped Ge/Si multi-layer heterostructures with incorporated Ge quantum dots (QDs) are studied. Calculations of the electronic band structure and luminescence measurements prove the existence of an electron miniband within the columns of the QDs. Miniband formation results in a conversion of the indirect to a quasi-direct excitons takes place. The optical transitions between electron states within the miniband and hole states within QDs are responsible for an intense luminescence in the 1.4–1.8 µm range, which is maintained up to room temperature. At 300 K, a light emitting diode based on such Ge/Si QD superlattices demonstrates an external quantum efficiency of 0.04% at a wavelength of 1.55 µm.

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Acknowledgments

We gratefully acknowledge helpful discussions with V. Kveder, D. Kovalev, G. Abstreiter and D. Grützmacher. We would like to thank A. Frommfeld for supporting the MBE growth and S. Schwirzke-Schaaf for contributions to Raman measurements. This work was supported by the EU project SANDiE (Network of Ecxellence, contract N. 500101). The Russian authors thank for support of the Russian Foundation of Basic Research (Grant N. 05-02-17780).